Field of the Invention
This invention relates to a process for the reclamation of elastomeric waste material to produce usable raw material. In one of its specific aspects, it relates to an improved process for reclaiming rubber.
Description of the Prior Art
Polymeric or plastic materials represent a significant waste disposal problem. For example, rubber reclaiming has become of particular interest because of the accumulation of large quantities of scrap tires which presents a major environmental problem.
Generally, the commercial processes for reclaiming vulcanized rubber depends on heating the rubber with rubber reclaiming solvents or oils. The heating is suitably conducted at the usual rubber reclaiming temperature of above 100.degree. C. and for a period to cause depolymerization or desulfurization to occur.
Scrap rubber to be reclaimed by the conventional reclamation processes is cut and ground into small pieces which are mechanically treated to remove fibrous materials which may be present in such scrap rubber, usually vulcanized as that obtained from old vehicular tire casings, rubber belts and the like. Following the removal of metallic and fibrous materials, the particulate rubber is subjected to heat (300.degree. to 500.degree. F.) and pressure (60 to 250 psi) in contact with a rubber reclaiming solvent or oil which serves to penetrate and swell the rubber and which assists materially in bringing it into condition for reworking. There are various types of rubber reclaiming solvents or oils which are used in conventional processes. Aliphatic hydrocarbon oils have been used with other hydrocarbon cuts which are chiefly aromatic and devoid of resin-forming components. Such conventional reclaiming solvents include coal tar naphthas, olefinic and/or aromatic fractions obtained from thermal or catalytic cracking operations, acid-soluble oils obtained from thermal or catalytic cracking operations, acid-soluble oils obtained from alkylation of isoparaffins with olefins and other hydrocarbon solvents generally boiling in the range of 225.degree. to 500.degree. F. However, most of the above solvents are now considered toxic to the environment.
U.S. Pat. No. 4,469,817 to Hayaski, et al proposes to obviate the necessity for process oils and to reduce the heating time in a reclaiming process by means of microwave heating of vulcanized rubber to a temperature for desulfurization (devulcanization) of rubber and upon completion of the desulfurization, quenching the desulfurized rubber to a temperature at which there is substantially no oxidation of the desulfurized rubber. However, the rate of cooling is critical and must be closely monitored and the devulcanization temperatures are high and range from about 180.degree. C. to 350.degree. C.
Japanese Application No. Sho 54 (1979) 126761 mentioned in the Hayaski et al patent discloses a method for the reclamation of vulcanized rubber comprising the steps of (a) classifying scrap vulcanized rubber by kind; (b) pulverizing the separated vulcanized rubber into powder; (c) admixing the pulverized vulcanized rubber with a conventional rubber process oil; (d) desulfurizing the vulcanized rubber powder by using microwave heating. According to the patent application the incorporation of the conventional rubber process oils minimizes the contact of the rubber molecules sufficiently to retard the oxidation of the rubber.
However, when large volumes of scrap vulcanized rubber are to be processed, according to this method the interior of the rubber mass does not expel the heat generated and the mass of rubber remains in an overheated state and induces undesirable side effects such as fracture of the molecules, decomposition of the rubber reclaiming solvents (process oils) and other components possible carbonization of the rubber and other components including the rubber reclaiming solvents.
Most of the aforementioned solvents and oils are considered toxic to humans and are a hazard to the environment. Thus, a process that provides for the reclaiming of waste rubber and/or plastic material to provide highly useful raw material on a commercial scale by a highly efficient and an environmentally safe process is most desirable.
An object of the present is to provide an improved and environmentally safe process for reclaiming elastomeric materials.
Another object of this invention is to provide an improved and environmentally safe rubber reclaiming process.
Another object of this invention is to provide an improved rubber reclaiming solvent.
Yet another object of this invention is to reduce the process time involved in the reclaiming of rubber.
Still another of object of this invention is to reduce any undesirable reaction products and provide for a useful high quality of raw material.